Can Morning Light Make You Thinner?

The claim: Throwing open the shades and basking in some sunlight first thing in the morning could help you maintain a healthy weight. According to a study published in PLOS One, people who got most of their daily exposure to even moderately bright light in the AM had significantly lower BMIs than those who got most of their exposure during later hours.

The research: Researchers from Northwestern University recruited 54 participants with an average age of 30 and, using wrist monitors, kept tabs on their light exposure, activity, and sleep patterns for seven days. They also followed participants' eating patterns via food logs. The findings: Even after controlling for all non-light exposure factors, the influence of morning light on weight was considerable—it accounted for roughly 20% of the subject’s BMIs, meaning those with earlier light exposure weighed less.Exposure light measuring 500 lux of brightness was the minimum threshold for having a lower BMI—outdoor light measures more than 1,000 lux even on a cloudy day. On a day with clear blue skies? Up to 100,000 lux. The news comes as research published in Endocrine Reviews suggests that nighttime light exposure (whether it’s coming from your smartphone, tablet, laptop, or TV) disrupts our natural circadian rhythms and contributes to rising obesity rates.

What it means: Modifying your exposure to light in terms of timing, duration, and intensity could help keep your waistline in check. The exact mechanism of how light affects body weight isn’t yet known, but study coauthor Kathy Reid, research associate professor of neurology at Northwestern’s Feinberg School of Medicine, says that light could have an impact on metabolism, hunger, and satiety.

The bottom line: Spending time in the sun may never outweigh the importance of diet and exercise, but it could be another weapon in your battle against the bulge. “People aren’t spending a lot of time in really bright light,” says Reid, “But light is clearly a strong signal to the body.” To reap it’s benefits, the researchers suggest getting at least 20 to 30 minutes of morning light between 8 AM and noon, every day. And don't forget your sunscreen—researchers believe the effect goes directly from the eye to the brain, so wearing sunscreen won't dampen the effect.